It is known to apply medicaments as sprays through the nose or mouth so that they are absorbed through the walls of the nasal passages or through the lungs. In order for the medicament to penetrate deep into the lung, for example into the alveolar sacs, it is considered necessary that the medicament particles or droplets have a mean size of less than 12 micrometres, for example from 1 to 5 micrometres. Whilst solid particles can be prepared with a mean size of less than 5 micrometres, problems are encountered in achieving such small sized droplets in a fluid spray.
Typically, such medicaments can be dispensed by means of bursts of large volumes of compressed air which entrain small amounts of the particulate to form a dust cloud or atomise some of a fluid to form a spray of fine droplets. However, this method results in losses of-medicament and requires that the user have a source of large volumes of compressed air available and this is impractical except in a hospital environment.
For self contained hand held devices, it has been the common practice to dispense the medicament as droplets or solid particles using a liquefied propellant medium to dispense the droplets or particles from a pressurised container through a mechanical breakdown device, for example a swirl chamber and spray nozzle orifice. Whilst such a system enables a self contained and readily portable device to be constructed, the use of liquefied propellants is increasingly unacceptable from environmental and other grounds.
Thus, the use of chlorofluorocarbon type propellants (CFCs) is to be phased out for most uses under the Montreal Protocol of 1987 due to their alleged effect on the ozone layer of the atmosphere. However, despite this, it was considered that there was no viable alternative to the use of CFC propellants for medicaments, and their use in this field has been permitted to continue.
Furthermore, whilst it would be desirable to put up the medicament in the form of a solution to aid absorption of the active ingredient into the blood stream, many medicaments are insoluble in CFCs. In order to achieve a solution it is necessary to use co-solvents and surface-active agents which may introduce undesirable secondary components into the medicament formulation. Moreover, when such solutions are sprayed, the resultant droplets lose their CFC component through rapid evaporation. As a result, the user inhales droplets of varying sizes travelling at different speeds as their size changes. The rapid evaporation of CFCs also gives the disadvantage that the user experiencing an uncomfortable chilling effect as he inhales the spray. On the other hand, it is the very rapid evaporation of liquefied propellants which enables them to generate the high pressures within the dispenser required to discharge material from the dispenser.
Despite these problems with the use of CFCs, they are still considered by the pharmaceutical industry to be the only practicable method for administering many forms of medicament. As recently as March 1990 a conference of leading experts in this field, the "Respiratory Drug Delivery II" Conference at Keystone, Colo., USA, did not contemplate that there was any other viable method of delivery for such drugs except the use of CFCs or their close analogues, such as the HFC and HCFC propellants.
In an attempt to overcome the problems associated with CFC propellants, there have been many proposals to adapt the mechanical pump type dispensers used to spray furniture polishes, hair lacquers and the like. In such devices a manually operated piston and cylinder or flexing diaphragm type of pump is operated by depressing an axial plunger or via a trigger type mechanism to force a fluid composition through a mechanical break up device, for example a swirl chamber and fine bore nozzle orifice, to form a spray of droplets without the use of a propellant gas or airstream. In general, the droplets formed are of a comparatively large size, typically 30 to 200 micrometres diameter; and the volume of the spray discharged at each operation of the pump is of little concern to the user.
In order for such devices to be suitable for use in dispensing a medicament, it is necessary to control both the droplet size, notably where the spray is to penetrate into the lungs of the user as stated above, and the amount of medicament dispensed so that each actuation of the pump will deliver a consistent dose of the medicament. It has therefore been proposed to incorporate some form of measured dose mechanism into the design of such pump spray devices. This is often provided in the form of the swept volume of the cylinder of the pump used to dispense the fluid, see for example U.S. Pat. Nos. 4,147,476 and 4,694,977 and PCT Application No. WO 87/04373. However, where the user does not for any reason operate the pump mechanism for its full stroke, the amount of fluid dispensed can vary significantly from the desired dosage.
Furthermore, it has not hitherto been considered possible to achieve the required very small droplet size consistently. A conventional hand operated pump type sprayer is typically operated by the user manually depressing the free end of the pump housing or plunger or a trigger mechanism so as to discharge fluid held in the pump, for example from the cylinder of the pump as the piston of the pump is driven up the cylinder, see for example U.S. Pat. Nos. 3,838,686, 4,693,675 and 4,694,977. However, not only is the pressure generated by the pump comparatively low, but the pressure generated will depend upon the speed at which the pump is operated and the strength of the user. As a result, the droplet size in the spray varies from operation to operation, even with the same person operating the pump.
It has been proposed to provide a spring against which the pump mechanism acts as fluid is drawn into the pump on the sucking stroke of the pump, for example into the cylinder as the piston is retracted in a piston/cylinder type of pump, see for example U.S. Pat. Nos. 3,471,065, 3,790,034, 3,797,748, 4,260,082, 4,183,449 and 4,345,718. The spring then provides a consistent driving force when released to drive the fluid out of the pump. In these proposals, the pump is designed so that fluid cannot escape from the cylinder until a release or outlet valve is operated. Therefore, the fluid is held within the pump under the pressure exerted by the compressed spring. When the valve is operated, the fluid is discharged from the pump under the action of the spring. Although this achieves a greater uniformity of the pressure at which the fluid is discharged, the fluid may be held under pressure within the pump before the outlet valve is operated. This can result in a number of problems. For example, the pump mechanism and outlet valve must be designed to resist the substantial pressures generated by the compressed spring, otherwise leakage may occur or the pump cylinder walls may rupture. Furthermore, where the pressure is retained for any length of time, some seepage of the fluid past the seals in the pump mechanism, for example past the seals between the piston and the cylinder wall, will occur, resulting in a loss of fluid and pressure from the cylinder. This will affect the volume of fluid dispensed and the droplet size in the spray which is eventually produced when the outlet valve is actuated. A further problem arises in that the user may not operate the pump mechanism for its full stroke. This will not only affect the volume of fluid dispensed, but will also affect the peak pressure achieved and hence the droplet size, since the spring will not be fully compressed.
In an alternative form of device proposed in U.S. Pat. No. 4,892,232, the fluid is held under pressure in a main container and a pre-determined quantity is transferred to a distendable rubber or similar sleeve carried by the valve actuator stem of the outlet valve to the container. The stem is provided with suitable porting so that the sleeve is connected to the remainder of the container when the stem is in the raised position. Fluid will thus flow under pressure from the container into the annular space between the sleeve and the stem wall to expand the sleeve radially. When the valve stem is depressed, the porting to the remainder of the container is closed and a port is opened allowing the fluid to escape from the annular space to a nozzle orifice as the sleeve is stretched axially and collapsed radially. Again, this device suffers from the problems of variable dose and variable droplet size due to variations in the speed and force used by the user in the depression of the valve stem and the extent to which the valve stem is moved.
We have devised a form of atomizer device which reduces the above problems and does not use a liquefied propellant or gas stream to discharge the contents of the device. Whilst the device is of particular use in the application of medicament fluids to the nasal passages or to the lungs, it can be used to apply a wide range of other materials where a simple self contained readily portable device is required.
In a preferred embodiment of the device of the invention the user imparts energy to an energy storage means which is retained in the "loaded" state until required to act upon a measured dose of the fluid to discharge it through a mechanical break up device or other discharge means. The fluid need not be held under pressure in the device, thus reducing some of the problems associated with earlier proposals. Since the "loading" of the energy storage means can be interlinked with the measurement of the dose of fluid, the operation of a latch or other means for retaining of the energy storage means in its "loaded" state can be used to ensure that the correct dose of fluid is achieved. The device of the invention thus substantially eliminates the problems encountered with prior proposals and provides a simple and effective means for producing sprays of fine sized droplets without the need for pressurised or liquefied propellant gasses.